German carmakers are being investigated over allegations that it’s been operating a price-fixing cartel since the early ’90s – activities that may have laid the foundations for the 2015 diesel emissions scandal, Der Spiegel claims.

A recent report in the magazine said antitrust authorities are examining allegations that executives from the country’s leading car makers colluded on technical specifications for everything from brakes to clutches and emissions systems. Over 200 employees from the leading manufacturers are said to have met some 60 times to hammer out the details.

Car stocks tumbled over the weekend as Volkswagen (VW), which owns the Porsche and Audi brands, as well as Germany’s cartel authority refused to comment on the report.

BMW has denied any wrongdoings, claiming, they have not “manipulated” any industry regulations.

“The fact is that automobiles from the BMW group are not manipulated and comply with the relevant legal requirements,” the company said in a statement, AFP reported.

“This of course also applies to diesel automobiles. This is confirmed by the relevant results from tests by national and international authorities,” the German automaker added.

“This new chapter in the diesel saga needs to be taken seriously,” Arndt Ellinghorst, an analyst with investment banking firm Evercore ISI, told Reuters. “Our conclusion is that there might be a risk of several hundred millions or even low billions.”

The report claims that representatives of VW, BMW, Audi and Porsche met regularly and even agreed on fitting their cars with small tanks for AdBlue, a type of solution that reduces the amount of nitrogen in exhaust fumes, instead of more costly large AdBlue tanks.

German car manufacturers have been reeling since Volkswagen admitted to exploiting loopholes in European Union regulations to cheat diesel emissions tests in 2015, meaning millions of diesel cars pumped much more nitrogen oxides into the air than the manufacturer claimed.

The US government has since issued international arrest warrants for five former Volkswagen managers in connection with the so-called dieselgate. The company also reached settlements with the US authorities, agreeing to pay a $2.8 billion criminal penalty, plus $1.5 billion in a civil lawsuit and another $11 billion to buy back cars and offer compensation.

Last week, Daimler announced a voluntary recall of more than three million Mercedes vehicles over its diesel engines while Audi said it would retrofit more than 800,000 diesel cars to improve their emissions in “real driving conditions.”

Der Spiegel reported Friday that both Volkswagen and Daimler have admitted to some of the allegations in the magazine’s investigation to the authorities.

Meanwhile, the European Commission and Europe’s antitrust investigative body, partially confirmed Saturday that they are investigating the case.

“The European Commission and the Bundeskartellamt [Germany’s federal cartel office] have received information on this matter, which is currently being assessed by the Commission,” the Commission reportedly told Deutsche Presse-Agnetur in a statement Saturday. “It is premature at this stage to speculate further.”

If found guilty, the European Commission has the power to fine the companies billions of euro and even force them to reform their business practices.